Exemplary embodiments relate to a nonvolatile memory device and, more particularly, to the page buffer circuit of a nonvolatile memory device and a method of operating the same, where the latches of a page buffer can store two verification results for one verification voltage.
A nonvolatile memory device may include a memory cell array, a row decoder, a page buffer unit, etc. The memory cell array may include a plurality of word lines elongated in rows, a plurality of bit lines elongated in columns, and a plurality of cell strings corresponding to the respective bit lines.
The row decoder, coupled to string selection lines, word lines, and a common source line, may be placed on one side of the memory cell array. Page buffers coupled to the plurality of bit lines are placed on the other side of the memory cell array.
Recently, to further increase the degree of integration of nonvolatile memory devices, active research is being done on a multi-bit cell which is able to store plural bits of data in a single memory cell. This type of a memory cell is called a multi-level cell (MLC). A memory cell capable of storing one bit is called a single level cell (SLC).
In the nonvolatile memory device, the number of latches for storing data when data are sensed or programmed is gradually increasing.
Furthermore, in a nonvolatile memory device using MLCs, it is important to narrow a distribution of the threshold voltages of the cells. To control the distribution of the threshold voltages, a variety of operation options, such as a double verification operation and a re-program operation, are being used, which increases the number of cases for performing a program operation.
In particular, in the case in which the double verification operation is performed, operations, such as precharging a bit line and sensing, are repeatedly performed in order to perform two verification operations using two verification voltages. Accordingly, the time that it takes to perform the verification operations is increased, leading to an increased time taken for a program operation to be executed.